1. Field of the Invention
The present invention relates to a control system for an internal combustion engine, and more particularly to a control system for an internal combustion engine including an exhaust gas recirculation mechanism for recirculating a certain amount of exhaust gases to an intake system.
2. Description of the Related Art
An intake air amount of an internal combustion engine, provided with a exhaust gas recirculation mechanism, is reduced by an amount of exhaust gas recirculated to an intake system of the engine. Therefore, there is a known technique for correcting a fuel supply amount according to an exhaust gas recirculation amount. In general, an exhaust gas recirculation control valve for controlling an exhaust gas recirculation amount opens with a time lag (a dead time period) with respect to a valve opening command signal. Therefore, in order to prevent the correction of a fuel supply amount or an ignition timing during a time when exhaust gases are not actually recirculated, a method of delaying the start of the above correction has been disclosed, for example, in Japanese Patent Laid-open No. Sho 60-169641. In this method, the start of the correction is delayed according to the dead time period from the time the valve opening command signal is output to the time the exhaust gas recirculation control valve actually starts to open. Similarly, a method of gradually changing a correction value from the time the valve opening command signal of the exhaust gas recirculation control valve is outputted, has been disclosed in Japanese Patent Laid-open No. Sho 59-192838.
The methods disclosed in the above-described publications, however, do not set a correction value corresponding to an actual lift amount (valve opening amount) of the exhaust gas recirculation control valve. To solve such a problem, a method of detecting a lift amount of the exhaust gas recirculation control valve and calculating a correction value of a fuel supply amount according to the detected lift amount, has been disclosed in Japanese Patent Laid-open No. Hei 7-127494. Further, a method of detecting a lift amount of the exhaust gas recirculation control valve and calculating a correction value of an ignition timing according to the detected lift amount, has been disclosed in Japanese Patent Laid-open No. Hei 7-119508.
According to the method of delaying the correction start timing, disclosed in Japanese Patent Laid-open No. Sho 60-169641 or the method of gradually changing the correction value, disclosed in Japanese Patent Laid-open No. Sho 59-192838, the improvement effect of the correction may not be sufficiently obtained, since the correction is not performed according to an actual lift amount of the exhaust gas recirculation control valve.
The methods disclosed in Japanese Patent Laid-open Nos. Hei 7-127494 and Hei 7-119508 have the following problem.
An exhaust gas recirculation control valve generally has a hysteresis characteristic as shown in FIG. 10. As shown by a solid line in this figure, when increasing a valve opening command signal LCMD, an actual lift amount LACT starts to increase from a time at which the LCMD value reaches a valve opening start command value LCMDH, and when decreasing the valve opening command signal LCMD, the valve is closed after the LCMD value reaches a valve closing command value LCMDL. In this way, at the time of valve opening, the actual lift amount LACT rapidly increases from the valve closed state, and thereafter, the actual lift amount LACT changes to follow the valve opening command signal LCMD. Accordingly, if a correction value of the fuel amount or the ignition timing is changed according to such a rapid change in the actual lift amount LACT, an air-fuel ratio of an air-fuel mixture to be supplied to the engine or the ignition timing rapidly changes. As a result, the exhaust characteristic and/or driveability of the engine often temporarily deteriorates.
An object of the present invention is to provide a control system for an internal combustion engine, which prevents a fuel supply amount correction value or an ignition timing correction value from rapidly changing when an actual lift amount of the exhaust gas recirculation control valve rapidly changes, and thereby maintaining desirable exhaust characteristics and/or driveability.
To achieve the above object, the present invention provides a control system for an internal combustion engine having an exhaust gas recirculation passage for recirculating a portion of exhaust gases from the engine to an intake system, and an exhaust gas recirculation control valve for controlling an amount of exhaust gases recirculated through the exhaust gas recirculation passage. The control system includes valve opening amount detecting means and fuel supply amount correcting means. The valve opening amount detecting means detects a valve opening amount of the exhaust gas recirculation control valve. The fuel supply amount correcting means corrects a fuel amount to be supplied to the engine according to the valve opening amount of the exhaust gas recirculation control valve. The fuel supply amount correcting means includes average value calculating means and correction value calculating means. The average value calculating means calculates an average valve opening value according the valve opening amount detected by the valve opening amount detecting means. A change rate of the average valve opening value is smaller than that of the valve opening amount detected by the valve opening amount detecting means. The correction value calculating means calculates a correction value for correcting the fuel supply amount according to the average valve opening value. The fuel supply amount correcting means corrects the fuel supply amount according to the calculated correction value from a time at which an opening of the exhaust gas recirculation control valve is detected by the valve opening amount detecting means.
With this configuration, an average valve opening value, a change rate of which is smaller than that of a valve opening amount detected by the valve opening amount detecting means, is calculated, and a correction value for correcting a fuel supply amount is calculated according to the average valve opening value. The correction of the fuel supply amount according to the correction value is started from the time the opening of the exhaust gas recirculation control valve is detected by the valve opening amount detecting means. Accordingly, it is possible to prevent the correction value of the fuel supply amount from being rapidly changed when the actual valve opening amount of the exhaust gas recirculation control valve rapidly changes, and hence to keep a desirable exhaust characteristic.
The present invention further provides a control system for an internal combustion engine having an exhaust gas recirculation passage for recirculating a portion of exhaust gases from the engine to an intake system and an exhaust gas recirculation control valve for controlling an amount of exhaust gases recirculated through the exhaust gas recirculation passage. The control system includes valve opening amount detecting means and ignition timing correcting means. The valve opening amount detecting means detects a valve opening amount of the exhaust gas recirculation control valve. The ignition timing correcting means corrects an ignition timing of the engine according to the valve opening amount of the exhaust gas recirculation control valve. The ignition timing correcting means includes average value calculating means and correction value calculating means. The average value calculating means calculates an average valve opening value according the valve opening amount detected by the valve opening amount detecting means. A change rate of the average valve opening value is smaller than that of the valve opening amount detected by the valve opening amount detecting means. The correction value calculating means calculates a correction value for correcting the ignition timing according to the average valve opening value. The ignition timing correcting means corrects the ignition timing according to the calculated correction value from a time at which an opening of the exhaust gas recirculation control valve is detected by the valve opening amount detecting means.
With this configuration, an average valve opening value, a change rate of which is smaller than that of a valve opening amount detected by the valve opening amount detecting means, is calculated, and a correction value for correcting an ignition timing is calculated according to the average valve opening value. The correction of the ignition timing according to the correction value is started from the time the opening of the exhaust gas recirculation control valve is detected by the valve opening amount detecting means. Accordingly, it is possible to prevent the correction value of the ignition timing from being rapidly changed when the actual valve opening amount of the exhaust gas recirculation control valve rapidly changes, and hence to keep a desirable driveability.
Preferably, the average value calculating means sets the change rate of the average valve opening value such that the change rate of the average valve opening value becomes smaller as the average valve opening value becomes smaller.
With this configuration, the change rate of the average valve opening value is set to become smaller as the average valve opening value becomes smaller. Accordingly, immediately after the opening of the exhaust gas recirculation control valve is started, the change rate of the average valve opening value is small, and as the valve opening amount increases, the change rate of the average valve opening value is increased to rapidly follow a change in the actual valve opening amount. As a result, it is possible to control the fuel supply amount or the ignition timing in accordance with the valve opening characteristic (see FIG. 10) of the exhaust gas recirculation control valve.
Other objects and advantages of the present invention will be apparent from the following description in conjunction with the accompanying drawings.